Process for the production of formic acid



Patented Dec. 3, 1935 PROCESS FOR THE PRODUCTION OF FORMIC ACID GilbertB. Carpenter, Bellemoor; Del., assignor to E. I. du Pont de Nemours &Company, Wilmington, Del., a corporation of Delaware No Drawing.Application August 24, 1931,

Serial No. 559,131- r 5 Claims.

This invention relates to a process for the preparation of formic acidfrom carbon monoxide and steam and is directed particularly to the useof a new catalyst for the reaction.

It has been known that carbon monoxide and steam will react, in thepresence of a suitable catalyst, to give formic acid. As this process isone which employs raw materials that are relatively inexpensive, itshould, under favorable conditions, produce the acid at an exceptionallylow cost. Its commercial success, however, will in no small part bedetermined by the catalyst used. Those which have been proposedheretofore have not been entirely satisfactory for commercial operationdue to low yield, short life, and other economic considerations. Effortsof investigators in this art have been directed, therefore, to thediscovery of catalysts having high activity and which, furthermore,favor the pro duction of formic acid while tending to inhibit theformation of undesirable side products.

An object of the present invention is to provide new catalysts for thepreparation of formic acid from carbon monoxide and steam having theabove desirable characteristics. Other objects will hereinafter appear.

According to the present invention formic acid can be prepared fromcarbon monoxide and steam by passing a mixture of these gases over acatalyst which comprises an acid salt (1. e. containing a replaceablehydrogen) of the acidic oxides of elements such as, for example,phosphorus, arsenic, tungsten, molybdenum, uranium, chromium, vanadium,boron, silicon, and zirconium, As examples of such catalysts myinvention covers the following and similar compounds; phosphates ofzinc, calcium, magnesium, sodium, potassium, copper, cerium, thorium,etc., and the acid salts formed between these metals and the oxides oftungsten, molybdenum, etc. These catalysts may be used alone or asadmixtures and may be either unsupported or supported upon the usualtype of catalyst support such, for example, as activated charcoal,fullers earth, kieselguhr, etc.

The carbon monoxide required for this synthesis may conveniently bederived from various commercial sources, such, as example, water-gas,producer gas, etc., by liquefaction or other methods, and shouldlikewise for the best results be relatively pure.

Inert gases, such as nitrogen, carbon dioxide, etc., may be includedwith the reactants, this being advantageous in some cases from thestandpoint of controlling the temperature of the exothermic reaction andof limiting the extent thereof, or it may be desired to restrict theoverall conversion of the reaction for the sake of enhancing therelative yield of formic acid.

I prefer generally to conduct the reaction at 5 pressures in excess ofatmospheric, say from 25 to 900 atmospheres. The reaction proceeds overa wide range of temperatures employing the above described catalysts,depending upon the gaseous composition employed. Generally the 10desired conversion of the carbon monoxide and steam to formic acid canbe obtained at a temperature of from IUD-400 C. although I generallyprefer to conduct the reaction in the range of from 200-300 C. 15

The following example will illustrate one method of practicing theinvention, although the invention is not limited thereto.

Example 1.A gaseous mixture consisting of 90 parts by volume of carbonmonoxide, and 0 parts by volume of steam is passed at a pressure of 700atmospheres and a temperature of 325 C. over an acid zinc phosphatecatalyst. This catalyst may be prepared by adding to an aqueousphosphoric acid solution a suitable amount of zinc oxide to form primaryzinc phosphate, Zn(H2PO4)2, and subsequently impregnating a support,such as activated charcoal, with this solution. After drying thecatalyst at approximately 120 C. itis ready for use. Upon condensationof the reaction product a condensate will be obtained containing formicacid.

Example 2.-A gaseous mixture comprising 95 parts by volume of carbonmonoxide and 20 parts by volume of steam is passed over a primarycalcium phosphate catalyst Ca(H2PO4) 2 at a pressure of 200 atmospheresand a temperature of approximately 325 C. A good yield of formic acidadmixed with other aliphatic carboxylic acids will be obtained.

The apparatus which may be employed for conducting the reaction may beof any conventional type and preferably one in which the temperature ofexothermic reactions can be readily controlled at the desiredtemperature. Owing to the corrosive action of formic acid, the interiorof the converter and conduits therefrom should preferably be protected.This may be accomplished by using glass or glass-lined apparatus or bycoating the inner surfaces of the apparatus with chromium or silver orusing for the construction of this equipment acid-resisting alloys of,for example, molybdenum, cobalt, tungsten, chromium, manganese, ornickel.

Various changes may be made in the method of employing the abovecatalysts for the preparation of formic acid from carbon monoxide andsteam without departing from this invention or sacrificing theadvantages that may be derived therefrom.

I claim:

1. In a process for the preparation of formic acid from a gaseousmixture of carbon monoxide and steam the step which comprises passingthe gaseous mixture over acatalyst comprising an acid salt of the acidicoxides of the elements selected from the group consisting of phosphorus,arsenic, tungsten, molybdenum, uranium, chromium, vanadium, boron,silicon and zirconium.

2. In a process for the preparation of formic acid from a" gaseousmixture of carbon monoxide and steam the step which comprises passingthe gaseous mixture over an acid metal phosphate catalyst.

3. In a process for the preparation of formic acid from a gaseousmixture of carbon monoxide and steam the step which comprises passingthe gaseous mixture over a calcium acid phosphate catalyst.

4. In a process for the preparation of formic acid from a gaseousmixture of carbon monoxide and steam the step which comprises passingthe gaseous mixture over an acid zinc phosphate catalyst.

5. In a process for the preparation of formic acid from a gaseousmixture of carbon monoxide and steam the step which comprises passingthe gaseous mixture over primary calcium phosphate catalyst.

GILBERT B. CARPENTER.

